1. FIELD OF THE INVENTION:
This invention relates to a flexible bilayered sheet of a base layer containing abrasive particles and a top layer containing metal or alloy matrix particles, a method for producing same, and a single layer composite coating produced therefrom.
2. PRIOR ART:
U.S. Pat. No. 3,743,556 teaches the production of coatings of abrasive metal particles in a metal or alloy matrix by contacting the substrate to be coated with a laminate of a base layer of abrasive particles in a voltilizable support such as polytetrafluoroethylene and an upper layer of matrix metal or alloy particles in a similar volatilizable support. Upon heating above the volatilization point of the support material, the support material is removed, and upon subsequent heating above the melting point of the matrix metal or alloy particles, the molten metal infiltrates the abrasive layer to form the desired "filled coating".
Advantages over the prior art coating techniques are said to include uniformity of coating, especially on a substrate having an intricate surface, and the avoidance of alternative methods such as plasma spraying, flame spraying, or dusting of abrasive and metal particles on the substrate to be coated.
The laminate layers are produced in accordance with the teachings of the patent either by mechanical working of a mixture of the particles with the polytetrafluoroethylene particles in order to fibrillate the polytetrafluoroethylene particles and to interleave the fibrils, followed by passing the worked mixture through pressure rolls spaced to produce a sheet of desired thickness. Alternatively, such layers are produced in accordance with the teachings of the patent by mixing the particles with shellac, polymethacrylate, polyacrylate or the like, and forming the resulting fluid mixture into a layer such as by doctoring directly onto the substrate to be coated.
While the first technique is advantageous in that it produces self-supporting sheets or layers, it is time consuming in requiring mechanical working and feeding through pressure rolls in order to form the layers or sheets. The second technique avoids the necessity for such processing steps, but does not enable the production of self-supporting sheets or layers. On the contrary, such layers must be formed directly on the substrate to be coated, and consequently a major advantage of the achievement of uniformity of coating on intricate surfaces is lost.